The present invention relates to the field of microfluidic circuitry for biochemical processes or reaction. It relates more specifically to the regulation of pressure and movement of gases into and out of microfluidic circuits.
The tools of microfabrication developed primarily by the integrated circuit and microsystems industries may be used to fabricate micrometer-sized structures that are designed to manipulate small volumes of fluids. This area of development is known as microfluidics. Microfluidic structures have been fabricated to integrate and miniaturize many of the fluid handling and analysis steps involved in traditional biological and chemical analysis. The present and forthcoming integrated and miniaturized systems are expected to offer several advantages over traditional methods. These advantages include greater quality control, faster analysis times, higher throughput of sample processing, and lower costs primarily related to smaller sample volumes and smaller amounts of chemicals and reagents required to analyze these smaller volumes.
Many different methods of fluid manipulation and sample analysis have and will be created. The numerous varying chemical and physical properties associated with the multitude of possible sample types make it difficult, if not impossible, for one sample manipulation or analysis technique to be used for all microfluidic applications. For example, there are many methods of pumping fluids through a microfluidic processing circuit, some of which are useful for ionic solutions, some of which are more appropriate for larger flow rates, and some of which utilize no moving parts. These include electrokinetics, electro-hydrodynamics, and pressure driven flow. Pressure driven flow can be further broken down into pneumatics, hydraulics, capillarity and centrifugal flow.
In most utilizations of pressure driven flow the microfluidic circuit is open to the atmosphere at one or more points downstream of the moving fluid so that air displaced by the moving fluid is allowed to escape the circuit. This prevents unwanted buildup of pressure that may oppose the desired fluid movement. The fluid may be prevented from escaping the circuit through the air displacement ducts by use of capillary valves, porous hydrophobic membranes, or similar methods, where air may escape but the fluid is contained.
The passive, or mostly passive, behavior of the air displacement ducts and possible corresponding capillary valves, are generally sufficient for their intended purpose. However, benefit may be gained by altering the pressure inside the microfluidic circuit, which cannot be readily carried out with passive air displacement ducts.
As the physical and chemical properties of a fluid, or the reaction rates of a reaction in which the fluid is involved, may vary with pressure, in some applications it would be beneficial for the fluid within a fluid circuit to experience a pressure higher or lower than the normal ambient pressure to which it is exposed via the air ducts.
Some reactions involve the production of gaseous phases that it is desirable to remove from the reaction chamber. This may be needed to prevent buildup of pressure within the system, to keep the gases from possibly poisoning further reactions, or to allow for analysis of the gases that are generated. In addition, some reactions may benefit from the delivery of gaseous materials, such as for the delivery of gaseous reagents, or for heating or cooling the system. Therefore, it would be desirable to provide a method for removing gaseous components from or introducing gaseous components to the microfluidic system.
The present invention discloses a method and system for manipulating the flow of gaseous materials into and out of a microfluidic circuit via air displacement ducts common in many pressure driven microfluidic systems. Air displacement ducts are used in combination with valves, pumps, and other pressure regulation devices to provide for the delivery or removal of gaseous reaction constituents or products, and to allow for the control of ambient pressure, and hence reaction pressure, within a microfluidic system. The air displacement ducts are not in direct communication with the atmosphere, but rather are connected to active pressure regulation devices such as valves and pumps that allow the air flow to be controlled through each duct individually, if desired. These active pressure regulation devices may be integrated within the microfluidic substrate, or they may be permanent or semi permanent members of an external system to which the microfluidic system is interfaced.
One object of the invention is to allow manipulation of the pressure within a microfluidic circuit in an effort to change the reaction process of a sample when compared to normal atmospheric conditions.
Another object of the invention is to allow for the delivery or removal of gaseous reactants or products from the microfluidic system, or simply to deliver hot or cold air to heat or cool a microfluidic sample. In most applications the air remaining in the fluid circuit is at approximately the same pressure as the ambient atmosphere, due to the presence of the air displacement ducts.